1. Field of the Invention
The present invention relates to a liquid crystal display technology, more particularly, to a liquid crystal display and a method of optical compensation thereof.
2. Description of the Related Art
With the growing popularity of liquid crystal display panels, the display quality requirements for liquid crystal display panels have become increasingly demanding. Take the thin film transistor liquid crystal display (TFT-LCD) as an example. As the observation angle of the TFT-LCD increases, the contrast of screen gradually decreases and the screen clarity also gradually decreases. This is because the birefringence of the liquid crystal molecules in the liquid crystal layer changes as the observation angle changes. As a result, a wide viewing angle compensation film is utilized to perform compensation so that dark-state light leakage is effectively reduced to greatly improve the contrast of the screen within a certain range of viewing angle.
The general compensation principle of the compensation film is to correct phase differences generated by liquid crystal at different viewing angle. Hence, the birefringence of the liquid crystal molecules is symmetrically compensated.
For different display modes for the liquid crystal display, the compensation films adopted are different. In a large-size LCD TV, the compensation film utilized is mostly for the vertical alignment (VA) display mode. During an early stage, N-TAC produced by Konica Corporation is adopted. Later, with the continuous development, products including Zeonor from Opotes Corporation, F-TAC series from Fujitsu, X-Plate from Nitto Denko, etc, are adopted.
For the same optical path difference of liquid crystal, the dark-state light leakage at a large viewing angle will differ and the contrast will also differ if the compensation value of the compensation film is different. Please refer to FIG. 1 and FIG. 2, FIG. 1 is schematic diagram of an isoluminance contour after dark-state light leakage is compensated by utilizing a uniaxial positive birefringence A-Plate and a uniaxial negative birefringence C-Plate according to the prior art. FIG. 2 is a schematic diagram of an equal contrast ratio contour at any viewing angle after being compensated by utilizing the A-Plate and the C-Plate according to the prior art. Compensation values for the above-mentioned A-Plate and the C-Plate are shown in the following table:
Optical pathdifference ofPretilt angle ofA-PlateA-PlateC-Plateliquid crystalliquid crystalRoRthRth333.5 nm89°109 nm55 nm403 nm
As shown in FIG. 1 and FIG. 2, it is not difficult to understand that, when the prior art A-Plate and C-Plate are adopted, their compensation values result in a severe dark-state light leakage phenomenon at a large viewing angle. The contrast at a large viewing angle becomes poor, and the range of viewing angle is small.
It is therefore very important to resolve the above-mentioned technical problems.